The subject matter disclosed herein relates to a method and system for biasing working fluid flow. More specifically, the subject matter herein relates to biasing steam flow to multiple condensing steam turbine sections.
Many smaller or medium sized thermal power plants are designed to supply each steam turbine condenser with coolant (water or air) directly from a coolant source (i.e., cooling tower, lake, ambient air, or river). However, some larger thermal power plants, such as those with four or more low pressure (LP) turbine expansions, are designed differently. In these larger plants, coolant is supplied to a first condenser connected to the first LP turbine, and then reused at its warmer state to cool a second condenser connected to the second LP turbine. After leaving the second condenser, the exhaust heat can be rejected to the ambient. This design may reduce coolant flow, thereby requiring less pump and/or fan power, and may reduce the average condensation pressure. Further, this design may reduce the size of required heat rejection equipment (i.e., cooling tower, air condenser, etc.) by increasing the heat rejection temperature.
While the above-described system may provide better performance than a design with direct coolant supply to each condenser, it still suffers from shortcomings. For example, where both the first LP turbine and the second LP turbine have the same exit annulus area, performance of the system may be less than optimal. In this case, the first LP turbine (receiving lower temperature coolant) will have a lower condenser pressure than the second LP turbine (receiving warmer coolant heated by exhaust from first LP turbine). These differences in condenser pressure lead to a higher exhaust velocity and greater exhaust loss at the first LP turbine, despite the fact that both the first LP turbine and the second LP turbine receive the same amount of steam flow. This may lead to compromised performance of the power plant.